def changed(event): print "something changed in ", event.region for ch in event.changes: ch.highlight() # highlight all changes sleep(1) for ch in event.changes: ch.highlight() # turn off the highlights with selectRegion("select a region to observe") as r: # any change larger than 50 pixels would trigger the changed function onChange(50, changed) observe(background=True) wait(30) # another way to observe for 30 seconds r.stopObserver()